There are 3 ways in which leads can be returned:
1) Via the leads screen by a User or Buyer
2) Via Import
3) Via the REST API
1) Via the leads screen by a user/buyer
You can return leads that have been marked as sold from the leads screen. Equally you can grant access to your Buyers to return leads (which can be auto-approved or subject to review). The most common reason for returning a lead(s) is due to it falling out of criteria set by the Buyer. You can of course avoid this by setting up rules in your portal to ensure that the leads being delivered are exactly on point :)
The Process for returning leads via the leads screen as a user
In the example below, we select a lead and select "return" from the drop down. The reason for the return is selected, the buyer (in this case there is more than 1) and that we want to reverse the payout to the supplier. This in tun will mark the lead as unsold and reverse the revenue and payout (to the supplier).
The Process for returning leads via the leads screen as a Buyer
The process is similar, however the screen options are limited. From their leads screen they will the select the lead(s) and return the lead with a reason. When this happens you will be notified within your portal. Returned leads by the Buyer can be found under Leads > Buyer Returns.
Remember, you will need to give the Buyer permission to Return Leads. At this stage you have the option to force them to be subject to approval (else they will auto-returned).
Filtering leads to show Returns
From the leads screen select the sold status as Returned.
How to add an additional return reason to the portal
In the example below, we navigate to the Admin > Lists page and add the reasons for return. When saved the new entry will be available from the dropdown (that is shown in the video above).